The role of adaptations in two-strain competition for sylvatic Trypanosoma cruzi transmission

This study presents a continuous-time model for the sylvatic transmission dynamics of two strains of Trypanosoma cruzi enzootic in North America, in order to study the role that adaptations of each strain to distinct modes of transmission (classical stercorarian transmission on the one hand, and vertical and oral transmission on the other) may play in the competition between the two strains. A deterministic model incorporating contact process saturation predicts competitive exclusion, and reproductive numbers for the infection provide a framework for evaluating the competition in terms of adaptive trade-off between distinct transmission modes. Results highlight the importance of oral transmission in mediating the competition between horizontal (stercorarian) and vertical transmission; its presence as a competing contact process advantages vertical transmission even without adaptation to oral transmission, but such adaptation appears necessary to explain the persistence of (vertically-adapted) T. cruzi IV in raccoons and woodrats in the southeastern United States.     

Effect of emulsified feeding of oily substrate via submerged ceramic membranes on surfactant production in <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> fermentation

Aqueous two-phase systems often face mass transfer limitations due to very poor miscibility of the fluids, and to enhance the homogeneity (or emulsification) in the reaction volume, high energy inputs are required which result in high shear forces in the culture medium. For the purposes of emulsification, microporous systems have advantages over other conventional methods due to mild operating conditions and narrow droplet-size distribution. In this study, emulsification within the culture volume was achieved by feeding the oily substrate (dispersed phase) into the aqueous medium (dispersion phase) via ceramic membranes integrated in the bioreactor. The method was investigated for bioprocesses aimed at producing rhamnolipids and polyhydroxyalkanoates (PHA). Better homogenization of the mixed volume and hence improved consumption of oily substrate was successful. Surfactants are produced by various bacterial cultures, especially Pseudomonas aeruginosa species, when oil is present as the only carbon source. Are surfactants produced only as a result of bacteria feeding on the oily substrate, or as a requirement to feed on the oily substrate, owing to their surface-active characteristics? This paper also intends to draw some conclusions in this respect.     

Rhamnolipid biosurfactants: evolutionary implications,applications and future prospects from untapped marine resource

Rhamnolipid-biosurfactants are known to be produced by the genus Pseudomonas, however recent literature reported that rhamnolipids (RLs) are distributed among diverse microbial genera. To integrate the evolutionary implications of rhamnosyl transferase among various groups of microorganisms, a comprehensive comparative motif analysis was performed amongst bacterial producers. Findings on new RL-producing microorganism is helpful from a biotechnological perspective and to replace infective P. aeruginosa strains which ultimately ensure industrially safe production of RLs. Halotolerant biosurfactants are required for efficient bioremediation of marine oil spills. An insight on the exploitation of marine microbes as the potential source of RL biosurfactants is highlighted in the present review. An economic production process, solid-state fermentation using agro-industrial and industrial waste would increase the scope of biosurfactants commercialization. Potential and prospective applications of RL-biosurfactants including hydrocarbon bioremediation, heavy metal removal, antibiofilm activity/biofilm disruption and greener synthesis of nanoparticles are highlighted in this review.     

The DIF1 gene of Arabidopsis is required for meiotic chromosome segregation and belongs to the REC8/RAD21 cohesin gene family

Cohesins are a group of conserved proteins responsible for cohesion between replicated sister chromatids during mitosis and meiosis and which are implicated in double-strand break repair and meiotic recombination. We describe here the identification and characterisation of an Arabidopsis gene - DETERMINATE, INFERTILE1 (DIF1), which is a homolog of the Schizosaccharomyces pombe REC8/RAD21 cohesin genes, and is essential for meiotic chromosome segregation. Five independent alleles of the DIF1 gene were isolated by transposon mutagenesis, and the mutants show complete male and female sterility. Pollen mother cells (PMCs) of dif1 mutants show multiple meiotic defects which are represented by univalent chromosomes and chromosome fragmentation at metaphase I, and acentric fragments and chromatin bridges in meiosis I and II. Consequently, chromosome segregation is strongly affected, resulting in meiotic products of uneven size, shape and of variable ploidy. The similarities in phenotype, and the sequence homology between DIF1 and the REC8/RAD21 cohesins suggests that cohesin function is largely conserved between eukaryotes and highlights the essential role cohesins play in plant meiosis.     

Large-scale analysis of yeast filamentous growth by systematic gene disruption and overexpression

Under certain conditions of nutrient stress, the budding yeast Saccharomyces cerevisiae initiates a striking developmental transition to a filamentous form of growth, resembling developmental transitions required for virulence in closely related pathogenic fungi. In yeast, filamentous growth involves known mitogen-activated protein kinase and protein kinase A signaling modules, but the full scope of this extensive filamentous response has not been delineated. Accordingly, we have undertaken the first systematic gene disruption and overexpression analysis of yeast filamentous growth. Standard laboratory strains of yeast are nonfilamentous; thus, we constructed a unique set of reagents in the filamentous Σ1278b strain, encompassing 3627 integrated transposon insertion alleles and 2043 overexpression constructs. Collectively, we analyzed 4528 yeast genes with these reagents and identified 487 genes conferring mutant filamentous phenotypes upon transposon insertion and/or gene overexpression. Using a fluorescent protein reporter integrated at the MUC1 locus, we further assayed each filamentous growth mutant for aberrant protein levels of the key flocculence factor Muc1p. Our results indicate a variety of genes and pathways affecting filamentous growth. In total, this filamentous growth gene set represents a wealth of yeast biology, highlighting 84 genes of uncharacterized function and an underappreciated role for the mitochondrial retrograde signaling pathway as an inhibitor of filamentous growth.     

SRA-Domain Proteins Required for DRM2-Mediated De Novo DNA Methylation

De novo DNA methylation and the maintenance of DNA methylation in asymmetrical sequence contexts is catalyzed by homologous proteins in plants (DRM2) and animals (DNMT3a/b). In plants, targeting of DRM2 depends on small interfering RNAs (siRNAs), although the molecular details are still unclear. Here, we show that two SRA-domain proteins (SUVH9 and SUVH2) are also essential for DRM2-mediated de novo and maintenance DNA methylation in Arabidopsis thaliana. At some loci, SUVH9 and SUVH2 act redundantly, while at other loci only SUVH2 is required, and this locus specificity correlates with the differing DNA-binding affinity of the SRA domains within SUVH9 and SUVH2. Specifically, SUVH9 preferentially binds methylated asymmetric sites, while SUVH2 preferentially binds methylated CG sites. The suvh9 and suvh2 mutations do not eliminate siRNAs, suggesting a role for SUVH9 and SUVH2 late in the RNA-directed DNA methylation pathway. With these new results, it is clear that SRA-domain proteins are involved in each of the three pathways leading to DNA methylation in Arabidopsis.     

Seminal plasma non-heparin binding proteins (NHBP) reduce the cryoinjury to buffalo cauda epididymal spermatozoa induced by heparin binding proteins (HBP)

Previous cryopreservation studies with buffalo cauda epididymal spermatozoa have reported a deleterious effect of seminal plasma heparin binding protein (HBP). The amount of HBP used in these studies was meager compared to the normal level of HBP in the buffalo ejaculate, still the damage induced upon the spermatozoa was substantial when compared to that incurred to the spermatozoa during routine freezing of ejaculated semen. Thus there might be some factor(s) in the seminal plasma, which reduce the deleterious effect of HBP on spermatozoa during cryopreservation of ejaculated semen. This study was conducted to investigate for the presence of any such factor in buffalo seminal plasma. Seminal plasma proteins were separated on their heparin binding properties as heparin binding (HBP) and non-heparin binding (NHBP). The separated proteins were added to the extender of buffalo cauda epididymal semen for cryopreservation either alone or in combination. The spermatozoa were assessed for progressive motility, viability, acrosomal integrity and response to hypo-osmotic solution test (HOST) at prefreeze and post-thaw stages of cryopreservation. NHBP was found to provide some degree of protection to buffalo spermatozoa against cryopreservation stress as well as the deleterious effect of HBP during cryopreservation.     

Use of Saccharum spontaneum (wild sugarcane) as biomaterial for cell immobilization and modulated ethanol production by thermotolerant Saccharomyces cerevisiae VS3

Saccharum spontaneum is a wasteland weed consists of 45.10 ± 0.35% cellulose and 22.75 ± 0.28% of hemicellulose on dry solid (DS) basis. Aqueous ammonia delignified S. spontaneum yielded total reducing sugars, 53.91 ± 0.44 g/L (539.10 ± 0.55 mg/g of substrate) with a hydrolytic efficiency of 77.85 ± 0.45%. The enzymes required for hydrolysis were prepared from culture supernatants of Aspergillus oryzae MTCC 1846. A maximum of 0.85 ± 0.07 IU/mL of filter paperase (FPase), 1.25 ± 0.04 IU/mL of carboxy methyl cellulase (CMCase) and 55.56 ± 0.52 IU/mL of xylanase activity was obtained after 7 days of incubation at 28 ± 0.5 °C using delignified S. spontaneum as carbon source under submerged fermentation conditions. Enzymatic hydrolysate of S. spontaneum was then tested for ethanol production under batch and repeated batch production system using “in-situ” entrapped Saccharomyces cerevisiae VS₃ cells in S. spontaneum stalks (1 cm × 1 cm) size. Immobilization was confirmed by the scanning electron microscopy (SEM). Batch fermentation of VS₃ free cells and immobilized cells showed ethanol production, 19.45 ± 0.55 g/L (yield, 0.410 ± 0.010 g/g) and 21.66 ± 0.62 g/L (yield, 0.434 ± 0.021 g/g), respectively. Immobilized VS₃ cells showed maximum ethanol production (22.85 ± 0.44 g/L, yield, 0.45 ± 0.04 g/g) up to 8th cycle during repeated batch fermentation followed by a gradual reduction in subsequent cycles of fermentation.